Method for improving sintering density and performance of powder metallurgy aluminum alloy

Abstract

The present invention relates to the technical field of aluminum alloy preparation by means of powder metallurgy. Provided is a method for improving the sintering density and performance of a powder metallurgy aluminum alloy. The method comprises short-flow process steps of preparation of a metal sulfide nano powder, preparation of a composite powder, pressing of green bodies, sintering, and heat treatment, wherein the metal sulfide nano powder is inlaid in the surface of an aluminum alloy powder, and reacts with a compact oxide film on the surface of the aluminum alloy powder during the sintering process to convert the oxide film from a continuous distribution state into several nanoscale alumina particles. Compared with other traditional methods, by adding a small amount of the metal sulfide nano powder to the aluminum alloy powder, which does not destroy the oxide film on the surface of the aluminum alloy powder by means of mechanical grinding, the method avoids the technical defects of mechanical grinding. By means of the method, nano alumina particles can be generated on the surface of the aluminum alloy powder; and sintering densification is achieved, strong plasticity is improved, the process flow is short, the cost is low, and the efficiency is high, thereby facilitating industrial large-scale production, popularization and use.

Description

A method for improving the sintering density and performance of powder metallurgy aluminum alloy Technical Field

[0001] The present invention relates to the technical field of preparing aluminum alloys by powder metallurgy, and in particular to a method for improving the sintering density and performance of powder metallurgy aluminum alloys. Background Art

[0002] High-strength aluminum alloys offer excellent properties such as light weight, high strength, high fracture toughness, and stress corrosion resistance, making them widely used in aerospace, defense, rail transportation, and new energy. However, the production of large-scale high-strength aluminum alloy ingots is hampered by problems such as coarse casting structure, alloy element segregation, and cracking caused by high residual stress.

[0003] Powder metallurgy, as a short-process, near-net-shape technology, offers multi-dimensional manufacturing advantages, ranging from small to large sizes and from simple shapes to complex structures. Furthermore, powder metallurgy boasts fine grains and a low tendency to crack, further improving the performance and yield of high-strength aluminum alloy ingots. However, an oxide film easily forms on the surface of aluminum powder, hindering mass transfer and, consequently, the sintering densification of the aluminum alloy powder.

[0004] Extensive research has been conducted both domestically and internationally to address the issue of oxide films hindering the densification of aluminum alloy powders during sintering. Ball milling is used to break up the oxide film on the powder surface, but a new oxide film quickly forms on the powder surface. Surface treatments like ball milling also affect the powder's surface roughness, microhardness, residual stress, and fatigue resistance. Active elements, with magnesium being the most ideal, are used to reduce residual and newly formed aluminum oxide. However, the increased oxygen content of magnesium powder, combined with the Kirkendall effect caused by elemental diffusion, prevents full densification during sintering.

[0005] Chinese patent CN104999074A discloses a method for improving the sintering density of aluminum alloy powder metallurgy parts. The method comprises using anhydrous ethanol as a solvent to prepare a boron oxide solution of a certain concentration, adding a certain mass of aluminum alloy powder to the solution, stirring evenly, and drying to obtain a surface-modified aluminum alloy powder. The powder is then formed and sintered. Although the density can be improved, it cannot achieve full density, and at high temperatures, boron oxide can chemically react with almost all metal oxides to form boron glass.

[0006] Chinese patent CN106670467A discloses a method for preparing a high-silicon aluminum alloy by peeling and hot extrusion of a rapidly solidified powder metallurgy high-silicon aluminum alloy. The finished high-silicon aluminum alloy is obtained through atomization powder making, screening, jacketing, peeling and hot extrusion, machining, solid solution, and aging. Not only is the silicon content very high, but the process is also complicated, the vacuum degassing process is difficult to operate, the cost is high, and the efficiency is low. The resulting high-silicon aluminum alloy bar is not suitable for the size and shape of powder metallurgy.

[0007] Chinese patent CN111906314A discloses a method for simultaneously improving the density and elongation of powder metallurgy materials. The method comprises the following steps: pressing raw powder into a shape to obtain a compact; placing the resulting compact into a graphite mold and placing the compact together in a hot pressing furnace, maintaining a vacuum state in the furnace chamber, and then sintering the finished product using a combination of low-temperature high-pressure and high-temperature low-pressure sintering method. The segmented pressure sintering method does not solve the problem of an oxide film hindering the sintering densification of aluminum alloy powder, and the problem of hindering mass transfer may still occur. In addition, the prepared aluminum alloy has relatively low tensile strength and relatively high plasticity.

[0008] Chinese patent CN113684391A discloses a method for preparing high-performance aluminum alloys and composite materials thereof, which requires densification and toughening through rotary forging. However, the size and shape of the prepared materials are limited, and the high-cost addition of reinforcement powder is required. The mixed powder is not subjected to heat treatment and sintering, but is directly machined. The oxide film on the surface of the aluminum alloy powder is physically destroyed. However, a new oxide film is generated after the destruction, and the surface properties of the aluminum alloy powder after the destruction are affected by hardness. As a result, the residual stress and fatigue properties of the aluminum alloy finally prepared are poor.

[0009] Therefore, it is urgent to develop an advanced technology that can achieve full densification of aluminum alloy powder sintering while ensuring the strength and plasticity of powder metallurgy aluminum alloy. Summary of the Invention

[0010] The technical problem to be solved by the present invention is that the density, strength and plasticity of current powder metallurgy aluminum alloys cannot be improved synergistically due to the oxide film on the surface of the aluminum alloy powder, and the existing mechanical grinding to destroy the oxide film will cause new generation after destruction, which will affect the surface roughness, microhardness, residual stress and fatigue resistance of the powder; or there is a technical defect that a fully dense powder metallurgy sintered aluminum alloy cannot be obtained by mechanically destroying the oxide film and adding active elements; or there are technical defects in destroying the oxide film by physical and chemical methods, such as complex procedures, difficult operation, high cost and low efficiency.

[0011] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0012] A method for improving the sintered density and performance of a powder metallurgy aluminum alloy, comprising the following process steps:

[0013] S1. Preparation of metal sulfide nanopowders

[0014] Preparation of high-purity metal sulfide nanopowders by low-temperature liquid phase rapid reaction method;

[0015] S2. Composite powder preparation

[0016] The high-purity metal sulfide nanopowder of S1 is dry-mechanically mixed with the aluminum alloy powder to obtain a composite powder in which the metal sulfide nanopowder is coated on the surface of the aluminum alloy powder;

[0017] S3. Pressing green body

[0018] The composite powder of S2 is formed by molding or cold isostatic pressing to obtain a pressed green body;

[0019] S4, sintering

[0020] The pressed green body of S3 is subjected to full-dense pressureless sintering to obtain a full-dense aluminum alloy sintered ingot;

[0021] S5. Heat treatment

[0022] The fully dense aluminum alloy sintered ingot of S4 is heat treated to obtain a high performance powder metallurgy aluminum alloy.

[0023] Preferably, the low-temperature liquid phase rapid reaction method in S1 is to dissolve elemental sulfur powder in carbon disulfide, then place the metal nanopowder in the above-mentioned sulfur-dissolved carbon disulfide solution and stir evenly, and the sulfur and the metal nanopowder react rapidly at 20-50°C to generate metal sulfide nanoparticles.

[0024] Preferably, the metal sulfide nanoparticles in S1 are suspended in a solution, and then ultrasonic stirring, centrifugation, and drying are performed to obtain metal sulfide nanopowder.

[0025] Preferably, the metal nanopowder in S1 is one or more of W, Mo, Mn, Cu, Zn, Sn, Sb, and In, and has an average particle size of 10-100 nm.

[0026] Preferably, the metal sulfide nanopowder and the aluminum alloy powder in S2 are prepared in a mass ratio of 1:1000-1:100.

[0027] Preferably, the aluminum alloy powder in S2 is one or more of gas atomized powder, air atomized powder, water atomized powder, water-gas combined atomized powder, and mechanical alloying powder, with an average particle size of 2-150 μm and a powder surface oxide film thickness of 3-20 nm.

[0028] Preferably, the dry mechanical mixing in S2 is one or more of rolling ball milling, planetary ball milling, stirring ball milling, vibration ball milling, V-type mixing, and three-dimensional mixing, the mixing time is 2-48 h, the ball-to-material ratio is 1:1-20:1, and the mixing atmosphere is one or both of nitrogen and argon.

[0029] Preferably, the molding pressure or cold isostatic pressing pressure in S3 is 100-500 MPa, and the holding time is 10-300 s.

[0030] Preferably, the fully dense pressureless sintering in S4 is one or more of vacuum sintering and atmosphere protection sintering, the sintering temperature is 450-630 ° C, the holding time is 0.5-5 h, the vacuum degree is 10 -3 -10 -1 Pa, the atmosphere is nitrogen, argon or both.

[0031] Preferably, the heat treatment in S5 is solution treatment at 450-550°C for 0.5-5 h, water quenching, and then aging at 120-190°C for 8-24 h.

[0032] Preferably, in the method for improving the sintering density and performance of powder metallurgy aluminum alloys, the tensile strength of the 7xxx series alloy is 508-653 MPa, the yield strength is 425-594 MPa, and the elongation is 4-8%; the tensile strength of the 2xxx series alloy is 310-488 MPa, the yield strength is 245-429 MPa, and the elongation is 5-8%.

[0033] Technical principle of the present invention:

[0034] First, a low-temperature liquid-phase rapid reaction method is used to prepare high-purity metal sulfide nanopowders. Aluminum alloy powder and nanometal sulfide powders are then mixed uniformly in a specific proportion to form a composite powder. This composite powder is then compacted and pressurelessly sintered to create a fully dense, high-performance powder metallurgy aluminum alloy. The metal sulfide nanopowders are embedded in the aluminum alloy powder surface. During sintering, they react with the dense oxide film on the aluminum alloy powder surface, transforming the film from a continuous distribution into nanometer-sized aluminum oxide particles. This creates a dispersed, reinforcing phase, transforming the oxide film into a beneficial one. This phase also opens up sintering mass transfer channels within the aluminum matrix, increasing the sintered density of the aluminum alloy and ultimately resulting in a high-performance powder metallurgy aluminum alloy.

[0035] Metal sulfide nanopowders are the core additive for achieving full densification during sintering of aluminum alloy powders. The nanometer size of the metal sulfide powder is crucial, as the synthesis process parameters determine its particle size. The reaction temperature between sulfur and metal nanopowders must be strictly controlled to achieve the desired result. If the temperature is too low, the reaction rate will be slow, affecting production efficiency. If the temperature is too high, the synthesized nanopowders will agglomerate, causing the powder particles to grow in size and potentially forming large particle inclusions, which will reduce the mechanical properties of the sintered aluminum alloy.

[0036] Among them, the pressureless sintering temperature, time, and atmosphere are important process conditions to ensure the transformation of the continuously distributed oxide film into dispersed nano-alumina particles. Only by mastering the appropriate pressureless sintering process parameters can the size and spatial distribution of alumina particles be accurately controlled, thereby hindering grain growth, increasing the room temperature and high temperature strength of the matrix, and improving the plasticity and toughness of the alloy.

[0037] Compared with the prior art, the above technical solution has at least the following beneficial effects:

[0038] The above scheme, the present invention proposes a method for improving the sintering density and performance of powder metallurgy aluminum alloy, which can solve the problem in the prior art that the oxide film of metallurgical aluminum alloy reduces the sintering density and performance, so that the density, strength and plasticity of the alloy can be significantly improved at room temperature and high temperature.

[0039] The present invention adds a small amount of metal sulfide nanopowder to aluminum alloy powder and utilizes sulfur element in the sintering process to break the continuous distribution of oxide film on the surface of aluminum alloy powder, thereby forming dispersed nano-aluminum oxide particles on the surface of aluminum alloy powder.

[0040] The method of the present invention does not require mechanical grinding to destroy the oxide film on the surface of the aluminum alloy powder. Instead, the metal sulfide nanopowder reacts with the continuous oxide film of the aluminum alloy powder to generate nano-alumina particles adhered to its surface, opening the sintering mass transfer channel of the aluminum matrix and promoting sintering densification. At the same time, the nano-alumina particles can play a dispersion strengthening role, further enhancing the strength of the sintered aluminum alloy and improving the plastic toughness.

[0041] The present invention simplifies the preparation process through pressureless sintering, has a short process flow, high production efficiency, and can realize large-scale industrial production. It has unique advantages in manufacturing complex-shaped, large-sized, high-strength aluminum alloy products, and has important application prospects in aerospace, national defense, military industry, rail transportation and other fields.

[0042] In summary, compared with other traditional methods, the method of the present invention creatively avoids destroying the oxide film on the surface of the aluminum alloy powder through mechanical grinding by adding a small amount of metal sulfide nanopowder to the aluminum alloy powder, thus avoiding the technical defects of mechanical grinding. It can generate nano-alumina particles on the surface of the aluminum alloy powder, sinter and densify it, improve strength and plasticity, and has a short process flow, low cost, and high efficiency, which is conducive to large-scale industrial production and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0044] FIG1 is a stress-strain curve of a 7075 aluminum alloy material prepared by a method for improving the sintering density and performance of a powder metallurgy aluminum alloy according to Example 1 of the present invention;

[0045] FIG2 is a stress-strain curve of a 7055 aluminum alloy material prepared by a method for improving the sintering density and performance of a powder metallurgy aluminum alloy according to Example 2 of the present invention;

[0046] FIG3 is a stress-strain curve diagram of a 2014 aluminum alloy material prepared by a method for improving the sintering density and performance of a powder metallurgy aluminum alloy according to Example 3 of the present invention. Implementation Method

[0047] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example 1

[0048] A method for improving the sintered density and performance of a powder metallurgy 7075 aluminum alloy, comprising the following process steps:

[0049] S1. Preparation of metal sulfide nanopowders

[0050] 10 g of elemental sulfur powder was dissolved in 200 ml of carbon disulfide solution and magnetically stirred at 20 °C for 1 h to obtain a uniformly mixed sulfur-containing carbon disulfide solution; 4 g of Cu metal nanopowder with an average particle size of 100 nm was placed in the aforementioned sulfur-containing carbon disulfide solution and stirred uniformly. The sulfur and metal nanopowder reacted rapidly at 20 °C to form metal sulfide nanoparticles. The metal sulfide nanoparticles were suspended in the solution and then subjected to ultrasonic stirring and centrifugal cleaning. The washed product was placed in a vacuum drying oven and vacuum dried at 60 °C for 2 h to completely remove the carbon disulfide liquid to obtain copper sulfide nanopowder;

[0051] S2. Composite powder preparation

[0052] The copper sulfide nanopowder of S1 and the 7075 aluminum alloy powder were mixed in a mass ratio of 1:500 and subjected to rolling ball milling at a rotation speed of 300 r / min, a mixing time of 24 h, a ball-to-material ratio of 1:1, and an argon atmosphere to obtain a composite powder in which the metal sulfide nanopowder was coated on the surface of the aluminum alloy powder; wherein the 7075 aluminum alloy powder was one or more of gas atomized powder, air atomized powder, water atomized powder, water-gas combined atomized powder, and mechanical alloying powder, with an average particle size of 36 μm and an oxide film thickness of 12 nm on the powder surface;

[0053] S3. Pressing green body

[0054] The S2 composite powder was formed by cold isostatic pressing. The composite powder was placed in a silica gel bag and vibrated, and the bag was sealed and placed in a cold isostatic press. The pressure was maintained at 200 MPa for 90 seconds to produce a pressed green body with a diameter of 600 mm and a height of 800 mm.

[0055] S4, sintering

[0056] The pressed green body of S3 was placed in a vacuum sintering furnace and kept at 350 °C for 2 h to allow the copper sulfide nanopowder to fully react with the surface of the 7075 aluminum alloy powder. Then the temperature was raised to 580 °C at a rate of 5 °C / min and the vacuum degree was 10 -2 Pa, holding time 3 h, to obtain fully dense aluminum alloy sintered ingot;

[0057] S5. Heat treatment

[0058] The fully dense aluminum alloy sintered ingot of S4 was solution treated at 470 ℃ for 2 h, water quenched, and then aged at 120 ℃ for 24 h to obtain high performance powder metallurgy 7075 aluminum alloy.

[0059] The high-performance powder metallurgy 7075 aluminum alloy prepared by the method for improving the sintering density and performance of powder metallurgy aluminum alloy described in this embodiment is shown in FIG1 , and has a tensile strength of 512 MPa, a yield strength of 436 MPa, and an elongation of 5.4%.

[0060] Example 2

[0061] A method for improving the sintered density and performance of a powder metallurgy 7055 aluminum alloy, comprising the following process steps:

[0062] S1. Preparation of metal sulfide nanopowders

[0063] 10 g of elemental sulfur powder was dissolved in 200 ml of carbon disulfide solution and magnetically stirred at 40 °C for 1 h to obtain a uniformly mixed sulfur-containing carbon disulfide solution; 5 g of Zn metal nanopowder with an average particle size of 30 nm was placed in the aforementioned sulfur-containing carbon disulfide solution and stirred uniformly. The sulfur and Zn metal nanopowder reacted rapidly at 40 °C to generate Zn metal sulfide nanoparticles. The Zn metal sulfide nanoparticles were suspended in the solution and then ultrasonically stirred and centrifuged for cleaning. The washed product was placed in a vacuum drying oven and vacuum dried at 60 °C for 2 h to completely remove the carbon disulfide liquid to obtain zinc sulfide nanoparticles.

[0064] S2. Composite powder preparation

[0065] The zinc sulfide nanopowder of S1 and the 7055 aluminum alloy powder were vibrated and ball-milled at a mass ratio of 1:100 for 2 h, with a ball-to-material ratio of 20:1 and an argon atmosphere to obtain a composite powder in which the metal sulfide nanopowder was coated on the surface of the aluminum alloy powder; wherein the 7055 aluminum alloy powder was one or more of gas atomized powder, air atomized powder, water atomized powder, water-gas combined atomized powder, and mechanical alloying powder, with an average particle size of 20 μm and an oxide film thickness of 15 nm on the powder surface;

[0066] S3. Pressing green body

[0067] The S2 composite powder was formed by cold isostatic pressing. The composite powder was placed in a silica gel bag and vibrated, then the bag was sealed and placed in a cold isostatic press. The pressure was maintained at 500 MPa for 30 seconds to produce a 500 mm × 400 mm × 60 mm pressed green body.

[0068] S4, sintering

[0069] The pressed green body of S3 was placed in a vacuum sintering furnace and first kept at 450 °C for 2 h to allow the copper sulfide nanopowder to fully react with the surface of the 7055 aluminum alloy powder. Then, the temperature was raised to 630 °C at a rate of 5 °C / min and kept at this temperature for 0.5 h to obtain a fully dense aluminum alloy sintered ingot.

[0070] S5. Heat treatment

[0071] The fully dense aluminum alloy sintered ingot of S4 was solution treated at 470 ℃ for 2 h, water quenched, and then aged at 120 ℃ for 24 h to obtain high performance powder metallurgy 7055 aluminum alloy.

[0072] The high-performance powder metallurgy 7055 aluminum alloy prepared by the method for improving the sintering density and performance of powder metallurgy aluminum alloy described in this embodiment is shown in FIG2 , and has a tensile strength of 569 MPa, a yield strength of 502 MPa, and an elongation of 5.2%.

[0073] Example 3

[0074] A method for improving the sintered density and performance of a powder metallurgy 2014 aluminum alloy, the method comprising the following process steps:

[0075] S1. Preparation of metal sulfide nanopowders

[0076] 20 g of elemental sulfur powder was dissolved in 300 ml of carbon disulfide solution and magnetically stirred at 50 °C for 1 h to obtain a uniformly mixed sulfur-containing carbon disulfide solution; 7 g of W metal nanopowder with an average particle size of 10 nm was placed in the aforementioned sulfur-containing carbon disulfide solution and stirred uniformly. Sulfur and W metal nanopowder reacted rapidly at 50 °C to generate W metal sulfide nanoparticles. The W metal sulfide nanoparticles were suspended in the solution and then subjected to ultrasonic stirring and centrifugal cleaning. The washed product was placed in a vacuum drying oven and vacuum dried at 60 °C for 2 h to completely remove the carbon disulfide liquid to obtain tungsten sulfide nanopowder;

[0077] S2. Composite powder preparation

[0078] The tungsten sulfide nanopowder of S1 and the 2014 aluminum alloy powder were mixed in a three-dimensional mixer at a mass ratio of 1:1000 for 48 h in a nitrogen atmosphere to obtain a composite powder in which the metal sulfide nanopowder was coated on the surface of the aluminum alloy powder. The 2014 aluminum alloy powder was air-atomized powder with an average particle size of 150 μm and an oxide film thickness of 20 nm.

[0079] S3. Pressing green body

[0080] The composite powder of S2 was molded by placing the composite powder into a steel mold and holding the mold at a pressure of 100 MPa for 300 s to produce a pressed green body with an outer diameter of 50 mm and a height of 28 mm.

[0081] S4, sintering

[0082] The pressed green body of S3 was placed in a nitrogen sintering furnace and first kept at 400 °C for 2 h to allow the tungsten disulfide nanopowder to fully react with the surface of the 2014 aluminum alloy powder. Then, the temperature was raised to 600 °C at a rate of 5 °C / min and kept at this temperature for 5 h to obtain a fully dense aluminum alloy sintered ingot.

[0083] S5. Heat treatment

[0084] The fully dense aluminum alloy sintered ingot of S4 was solution treated at 505 ℃ for 2 h, water quenched, and then aged at 178 ℃ for 24 h to obtain high performance powder metallurgy 2014 aluminum alloy.

[0085] The high-performance powder metallurgy 2014 aluminum alloy prepared by the method for improving the sintering density and performance of powder metallurgy aluminum alloy described in this embodiment is shown in FIG3 , and has a tensile strength of 387 MPa, a yield strength of 316 MPa, and an elongation of 6.5%.

[0086] Example 4

[0087] A method for improving the sintered density and performance of a powder metallurgy aluminum alloy, comprising the following process steps:

[0088] S1. Preparation of metal sulfide nanopowders

[0089] Elemental sulfur powder is dissolved in a carbon disulfide solution, and then Mo metal nanopowder with an average particle size of 30 nm is placed in the aforementioned sulfur-dissolved carbon disulfide solution and stirred evenly. The sulfur and metal nanopowder react rapidly at 50°C to form metal sulfide nanoparticles. The metal sulfide nanoparticles are suspended in the solution, and then ultrasonic stirring, centrifugation, and drying are required to obtain metal sulfide nanopowder.

[0090] S2. Composite powder preparation

[0091] High-purity metal sulfide nanopowder of S1 and 2024 aluminum alloy powder were mixed in a mass ratio of 1:200 and subjected to stirring ball milling for 36 h. The mixing atmosphere was argon gas, and the ball-to-material ratio was 10:1. The obtained composite powder was composed of metal sulfide nanopowder coated on the surface of aluminum alloy powder. The 2024 aluminum alloy powder was water-atomized powder with an average particle size of 15 μm and an oxide film thickness of 3 nm.

[0092] S3. Pressing green body

[0093] The composite powder of S2 was formed by cold isostatic pressing with a forming pressure of 200 MPa and a holding time of 200 s to obtain a pressed green body;

[0094] S4, sintering

[0095] The pressed green body of S3 was vacuum sintered at a temperature of 590 °C, a holding time of 4 h, and a vacuum degree of 10 -3 Pa, a fully dense aluminum alloy sintered ingot is obtained;

[0096] S5. Heat treatment

[0097] The fully dense aluminum alloy sintered ingot of S4 was solution treated at 490 ℃ for 0.5 h, water quenched, and then aged at 190 ℃ for 10 h to obtain a high-performance powder metallurgy aluminum alloy.

[0098] The high-performance powder metallurgy 2024 aluminum alloy prepared by the method for improving the sintering density and performance of powder metallurgy aluminum alloy described in this embodiment has a tensile strength of 488 MPa, a yield strength of 429 MPa, and an elongation of 5%.

[0099] Example 5

[0100] A method for improving the sintered density and performance of a powder metallurgy aluminum alloy, comprising the following process steps:

[0101] S1. Preparation of metal sulfide nanopowders

[0102] Elemental sulfur powder is dissolved in a carbon disulfide solution, and then Mn metal nanopowder with an average particle size of 80 nm is placed in the aforementioned sulfur-dissolved carbon disulfide solution and stirred evenly. The sulfur and metal nanopowder react rapidly at 40°C to form metal sulfide nanoparticles. The metal sulfide nanoparticles are suspended in the solution, and then ultrasonic stirring, centrifugation, and drying are required to obtain metal sulfide nanopowder.

[0103] S2. Composite powder preparation

[0104] The high-purity metal sulfide nanopowder of S1 and 7050 aluminum alloy powder were vibrated and ball-milled at a mass ratio of 1:400. The ball-milling time was 40 h, the ball-to-material ratio was 10:1, and the protective atmosphere was argon gas. Composite powders with metal sulfide nanopowder coated on the surface of aluminum alloy powder were obtained. Among them, the 7050 aluminum alloy powder was a water-gas atomized powder with an average particle size of 2 μm and an oxide film thickness of 8 nm on the powder surface. S3 and pressed green body

[0105] The composite powder of S2 was molded by die pressing at a pressure of 400 MPa and a holding time of 40 s to obtain a pressed green body.

[0106] S4, sintering

[0107] The pressed green body of S3 was sintered under argon protection at a temperature of 630 °C for 2 h to obtain a fully dense aluminum alloy sintered ingot.

[0108] S5. Heat treatment

[0109] The fully dense aluminum alloy sintered ingot of S4 was solution treated at 485 ℃ for 1 h, water quenched, and then aged at 125 ℃ for 18 h to obtain a high performance powder metallurgy aluminum alloy.

[0110] The high-performance powder metallurgy 7050 aluminum alloy prepared by the method for improving the sintering density and performance of powder metallurgy aluminum alloy described in this embodiment has a tensile strength of 549 MPa, a yield strength of 480 MPa, and an elongation of 6.3%.

[0111] Example 6

[0112] A method for improving the sintered density and performance of a powder metallurgy aluminum alloy, comprising the following process steps:

[0113] S1. Preparation of metal sulfide nanopowders

[0114] Elemental sulfur powder is dissolved in a carbon disulfide solution, and then Sn metal nanopowder with an average particle size of 50 nm is placed in the aforementioned sulfur-dissolved carbon disulfide solution and stirred evenly. The sulfur and metal nanopowder react rapidly at 20°C to form metal sulfide nanoparticles. The metal sulfide nanoparticles are suspended in the solution, and then ultrasonic stirring, centrifugation, and drying are required to obtain metal sulfide nanopowder.

[0115] S2. Composite powder preparation

[0116] High-purity metal sulfide nanopowder of S1 and Al-11.5%Zn-3.4%Mg-1.7%Cu (mass fraction) aluminum alloy powder were planetarily ball milled at a mass ratio of 1:100 for 30 h at a ball-to-powder ratio of 10:1 under nitrogen as a protective atmosphere to obtain a composite powder with metal sulfide nanopowder coated on the surface of the aluminum alloy powder. The Al-11.5%Zn-3.4%Mg-1.7%Cu aluminum alloy powder was nitrogen atomized powder with an average particle size of 44 μm and an oxide film thickness of 6 nm on the powder surface.

[0117] S3. Pressing green body

[0118] The composite powder of S2 was formed by cold isostatic pressing with a forming pressure of 300 MPa and a holding time of 120 s to obtain a pressed green body.

[0119] S4, sintering

[0120] The pressed green body of S3 was vacuum sintered at a temperature of 550 °C, a holding time of 5 h, and a vacuum degree of 10 -1 Pa, a fully dense aluminum alloy sintered ingot is obtained;

[0121] S5. Heat treatment

[0122] The S4 fully dense aluminum alloy sintered ingot was solution treated at 485℃ for 5 h, water quenched, and then aged at 120℃ for 24 h to obtain a high performance powder metallurgy aluminum alloy.

[0123] The high-performance powder metallurgy Al-11.5%Zn-3.4%Mg-1.7%Cu aluminum alloy prepared by the method for improving the sintering density and performance of powder metallurgy aluminum alloy described in this embodiment has a tensile strength of 653 MPa, a yield strength of 594 MPa, and an elongation of 4%.

[0124] The above scheme, the present invention proposes a method for improving the sintering density and performance of powder metallurgy aluminum alloy, which can solve the problem in the prior art that the oxide film of metallurgical aluminum alloy reduces the sintering density and performance, so that the density, strength and plasticity of the alloy can be significantly improved at room temperature and high temperature.

[0125] The present invention adds a small amount of metal sulfide nanopowder to aluminum alloy powder and utilizes sulfur element in the sintering process to break the continuous distribution of oxide film on the surface of aluminum alloy powder, thereby forming dispersed nano-aluminum oxide particles on the surface of aluminum alloy powder.

[0126] The method of the present invention does not require mechanical grinding to destroy the oxide film on the surface of the aluminum alloy powder. Instead, the metal sulfide nanopowder reacts with the continuous oxide film of the aluminum alloy powder to generate nano-alumina particles adhered to its surface, opening the sintering mass transfer channel of the aluminum matrix and promoting sintering densification. At the same time, the nano-alumina particles can play a dispersion strengthening role, further enhancing the strength of the sintered aluminum alloy and improving the plastic toughness.

[0127] The present invention simplifies the preparation process through pressureless sintering, has a short process flow, high production efficiency, and can realize large-scale industrial production. It has unique advantages in manufacturing complex-shaped, large-sized, high-strength aluminum alloy products, and has important application prospects in aerospace, national defense, military industry, rail transportation and other fields.

[0128] In summary, compared with other traditional methods, the method of the present invention adds a small amount of metal sulfide nanopowder to the aluminum alloy powder, creatively avoids destroying the oxide film on the surface of the aluminum alloy powder through mechanical grinding, avoids the technical defects of mechanical grinding, can generate nano-alumina particles on the surface of the aluminum alloy powder, sintering densification, improve strength and plasticity, has a short process flow, low cost, high efficiency, and is conducive to large-scale industrial production and promotion.

[0129] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for improving the sintering density and performance of powder metallurgy aluminum alloy, characterized in that: The method for improving the sintering density and performance of powder metallurgy aluminum alloy comprises the following process steps: S1. Preparation of metal sulfide nanopowders Preparation of high-purity metal sulfide nanopowders by low-temperature liquid phase rapid reaction method; S2. Composite powder preparation The high-purity metal sulfide nanopowder of S1 and the aluminum alloy powder are dry-mixed mechanically to obtain a composite powder in which the metal sulfide nanopowder is coated on the surface of the aluminum alloy powder; S3. Pressing green body The composite powder of S2 is formed by molding or cold isostatic pressing to obtain a pressed green body; S4, Sintering The pressed green body of S3 is subjected to full-dense pressureless sintering to obtain a full-dense sintered aluminum alloy ingot; S5. Heat treatment The fully dense aluminum alloy sintered ingot of S4 is heat treated to obtain a high performance powder metallurgy aluminum alloy.

2. The method for improving the sintering density and performance of powder metallurgy aluminum alloy according to claim 1, characterized in that: The low-temperature liquid phase rapid reaction method in S1 is to dissolve elemental sulfur powder in carbon disulfide, then place the metal nanopowder in the above sulfur-dissolved carbon disulfide solution and stir evenly, and the sulfur and the metal nanopowder react rapidly at 20-50°C to generate metal sulfide nanoparticles.

3. The method for improving the sintering density and performance of powder metallurgy aluminum alloy according to claim 2, characterized in that: The metal sulfide nanoparticles in S1 are suspended in the solution, and then need to be ultrasonically stirred, centrifuged, and dried to obtain metal sulfide nanopowder.

4. The method for improving the sintering density and performance of powder metallurgy aluminum alloy according to claim 2, characterized in that: The metal nanopowder in S1 is one or more of W, Mo, Mn, Cu, Zn, Sn, Sb, and In, and has an average particle size of 10-100 nm.

5. The method for improving the sintering density and performance of powder metallurgy aluminum alloy according to claim 1, characterized in that: In S2, the metal sulfide nanopowder and the aluminum alloy powder are prepared in a mass ratio of 1:1000-1:

100.

6. The method for improving the sintering density and performance of powder metallurgy aluminum alloy according to claim 1, characterized in that: The aluminum alloy powder in S2 is one or more of gas atomized powder, air atomized powder, water atomized powder, water-gas combined atomized powder, and mechanical alloying powder, with an average particle size of 2-150 μm and a powder surface oxide film thickness of 3-20 nm.

7. The method for improving the sintering density and performance of powder metallurgy aluminum alloy according to claim 1, characterized in that: The dry mechanical mixing in S2 is one or more of rolling ball milling, planetary ball milling, stirring ball milling, vibration ball milling, V-type mixing, and three-dimensional mixing. The mixing time is 2-48 h, the ball-to-material ratio is 1:1-20:1, and the mixing atmosphere is one or both of nitrogen and argon.

8. The method for improving the sintering density and performance of powder metallurgy aluminum alloy according to claim 1, characterized in that: In S3, the molding or cold isostatic pressing pressure is 100-500 MPa, and the holding time is 10-300 s.

9. The method for improving the sintering density and performance of powder metallurgy aluminum alloy according to claim 1, characterized in that: The fully dense pressureless sintering in S4 is one or more of vacuum sintering and atmosphere protection sintering. The sintering temperature is 450-630 ℃, the holding time is 0.5-5 h, and the vacuum degree is 10 -3 -10 -1 Pa, the atmosphere is nitrogen, argon or both.

10. The method for improving the sintering density and performance of powder metallurgy aluminum alloy according to claim 1, characterized in that: The heat treatment in S5 is solution treatment at 450-550 °C for 0.5-5 h, water quenching, and then aging at 120-190 °C for 8-24 h.

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